Effects of x-ray irradiation on polycrystalline silicon, thin-film transistors

Li, Yixin; Antonuk, Larry E.; El‐Mohri, Youcef; Zhao, Qihua; Du, Hong; Sawant, Amit; Wang, Yi

doi:10.1063/1.2179149

Cited by 52 publications

(43 citation statements)

References 44 publications

(39 reference statements)

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“…Poly-Si offers electron and hole mobilities approximately two and four orders of magnitude greater, respectively, than those of a-Si:H, overcoming many of the disadvantages of that material. In addition, poly-Si transistors have demonstrated good radiation tolerance (Li et al , 2006). Prototype active pixel imagers incorporating in-pixel amplification based on poly-Si TFTs have demonstrated over an order of magnitude increase in signal, as well as the ability to perform advanced readout techniques (El-Mohri et al , 2009).…”

Section: Introductionmentioning

confidence: 99%

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

et al. 2016

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Photon counting arrays (PCAs), defined as pixelated imagers which measure the absorbed energy of x-ray photons individually and record this information digitally, are of increasing clinical interest. A number of PCA prototypes with a 1 mm pixel-to-pixel pitch have recently been fabricated with polycrystalline silicon (poly-Si) — a thin-film technology capable of creating monolithic imagers of a size commensurate with human anatomy. In this study, analog and digital simulation frameworks were developed to provide insight into the influence of individual poly-Si transistors on pixel circuit performance — information that is not readily available through empirical means. The simulation frameworks were used to characterize the circuit designs employed in the prototypes. The analog framework, which determines the noise produced by individual transistors, was used to estimate energy resolution, as well as to identify which transistors contribute the most noise. The digital framework, which analyzes how well circuits function in the presence of significant variations in transistor properties, was used to estimate how fast a circuit can produce an output (referred to as output count rate). In addition, an algorithm was developed and used to estimate the minimum pixel pitch that could be achieved for the pixel circuits of the current prototypes. The simulation frameworks predict that the analog component of the PCA prototypes could have energy resolution as low as 8.9% FWHM at 70 keV; and the digital components should work well even in the presence of significant TFT variations, with the fastest component having output count rates as high as 3 MHz. Finally, based on conceivable improvements in the underlying fabrication process, the algorithm predicts that the 1 mm pitch of the current PCA prototypes could be reduced significantly, potentially to between ~240 and 290 μm.

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Section: Introductionmentioning

confidence: 99%

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

et al. 2016

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“…23 Poly-Si offers the advantage of substantially higher carrier mobilities, on the order of 100 cm 2 / V s for both electrons and holes, while maintaining the large area processing capability and radiation damage resistance of a-Si. 24 Such high mobilities enable faster TFT switching speeds and higher currents, as well as considerably more sophisticated amplification circuits based on both n-channel and p-channel TFTs. Another advantage of the high mobilities of poly-Si is the possibility of integrating additional circuitry, such as gate line drivers and data line multiplexers, on the periphery of AMFPI array substratesreducing the density of connections as well as the amount of peripheral external electronics.…”

Section: Introductionmentioning

confidence: 99%

“…Studies performed on such test circuits to investigate the radiation damage and noise properties of poly-Si TFTs have been previously reported. 24,27 In addition to providing a measure of the quality and performance of the poly-Si TFTs independent of the complications of array operation, empirical data obtained from these test circuits can also serve as input to circuit models simulating the signal and noise performance of array pixels. 27 The creation of these poly-Si arrays involves a hybrid process 28,29 employing a continuous a-Si photodiode structure and one to five poly-Si TFTs per pixel.…”

Section: Iia Introduction To Prototype Psi Arraysmentioning

confidence: 99%

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

El‐Mohri¹,

Antonuk²,

Koniczek³

et al. 2009

Medical Physics

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Active matrix, flat-panel imagers ͑AMFPIs͒ employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel ͑AP͒ architectures, using polycrystalline-silicon ͑poly-Si͒ TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n-and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array ͑PSI-1͒ that employs a pixel architecture with a single TFT, as well as two arrays ͑PSI-2 and PSI-3͒ that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of ϳ10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill factors that are close to unity. In addition, the greater complexity of PSI-2 and PSI-3 pixel circuits, compared to that of PSI-1, has no observable effect on spatial resolution. Both PSI-2 and PSI-3 exhibit high levels of additive noise, resulting in no net improvement in the signal-to-noise performance of these early prototypes compared to conventional AMFPIs. However, faster readout rates, coupled with implementation of multiple sampling protocols allowed by the nondestructive nature of pixel readout, resulted in a significantly lower noise level of ϳ560 e ͑rms͒ for PSI-3.

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“…There is significant interest for implementation of thin film transistors (TFTs) in irradiation environment [1][2][3][4]. Generally, there is insufficient research in this direction, including gate insulator which is the most sensitive component of TFTs [5,6].…”

Section: Introductionmentioning

confidence: 99%

Defect generation in non-nitrided and nitrided sputtered gate oxides under post-irradiation Fowler–Nordheim constant current stress

Jelenković

Kovačević

Jha

et al. 2013

Microelectronic Engineering

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Effects of x-ray irradiation on polycrystalline silicon, thin-film transistors

Cited by 52 publications

References 44 publications

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

Defect generation in non-nitrided and nitrided sputtered gate oxides under post-irradiation Fowler–Nordheim constant current stress

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